Joint replacement methods and apparatus

ABSTRACT

Apparatus and surgical techniques provide alternative cutting fixtures and other features to improve bone resection accuracy and joint stability. According to one embodiment, stabilizers are removably attached to a cutting guide to temporarily lengthen the surface against which a saw or other cutting device rests. Another embodiment provides differently shaped saw blades, having curved distal ends and right-angle bends applicable to box cuts of the type associated with cruciate sacrifice knee-replacement surgery. Methods are also disclosed whereby the box cuts, distal and posterior augment cuts may be approached from a distal perspective, both laterally and medially. A different embodiment provides a trial/cutting guide having flat surfaces as opposed to curved surfaces adapted for articulation within a joint. Yet a further alternative embodiment teaches a device for determining the joint line relative to a tibia using the fibula as reference.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Pat. application Ser. No.09/159,168, filed Sep. 23 1998, now U.S. Pat. No. 6,488,687 which claimsbenefit of U.S. provisional application No. 60/059,804, filed Sep. 23,1997; and the current application is a continuation-in-part of U.S. Pat.application Ser. No. 09/300,665, filed Apr. 27, 1999 now U.S. Pat. No.6,602,259 which is a continuation of U.S. Pat. application Ser. No.08/937,216, filed Sep. 18, 1997, now U.S. Pat. No. 5,897,559.

FIELD OF THE INVENTION

This invention concerns arthroplasty, and, more particularly, resides inimproved cutting guides and techniques to better assist a surgeon inpreparing a bone, for example, to receive an implant.

BACKGROUND OF THE INVENTION

Whether for primary or revision arthroplasty, cutting guides aretypically employed to ensure that the bone saw performs resectionscorresponding to mating surfaces of the prosthetic component. Forexample, in a femoral knee replacement, cutting guides or blocks aretemporarily secured to the distal end of the femoral shaft, and includeslots into which the blade of an oscillating saw is inserted to shapethe end of the bone in accordance with corresponding surfaces of theprosthetic element.

In the case of a revision, the procedure is usually more elaborate dueto deterioration of the previously prepared surfaces resulting fromdecomposition of the bone/prosthesis interface, necrosis, and otherfactors. Cutting blocks are also typically used in revision procedures,though bone deficiency often renders stabilization of the blockimpossible. In addition, if the cutting block includes a stem, thepositioning of the stemmed implant can alter the fit of the finalprosthesis relative to the bone. More recently introduced techniquesattempt to base the cuts on an intramedullary guide to which additionalcutting blocks are mounted. Though such approaches improve bone cuttingaccuracy, there remains an unacceptable margin of error, the correctionof which in some cases requiring a freehand shaping of the bone.

SUMMARY OF THE INVENTION

This invention extends and, in certain instances, improves upon,apparatus and methods disclosed and claimed in U.S. Pat. No. 5,716,361,which relates to combination trial/cutting guides, and methods of usingthe same, in various orthopedic joint situations such as the knee, hip,shoulder, and other areas of the body. The present invention is directedtoward apparatus and surgical techniques which augment or supplantcertain teachings of the '361 patent with respect to alternative cuttingfixtures and resection accuracy and stability.

One embodiment provides stabilizers which are removably attached to acutting guide so as to temporarily lengthen the surface against which asaw or other cutting device rests. Another embodiment providesdifferently shaped saw blades, having curved distal ends and right-anglebends applicable to box cuts of the type associated withcruciate-sacrifice knee-replacement surgery. Methods are also disclosedwhereby the box cuts, distal and posterior augment cuts may beapproached from a distal perspective, both laterally and medially. Adifferent embodiment provides a trial/cutting guide having flat surfacesas opposed to curved surfaces adapted for articulation within a joint.Yet a further alternative embodiment teaches a device for determiningthe joint line relative to a tibia using the fibula as reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing which shows the use of stabilizers removablyattached to a cutting guide to temporarily lengthening the surfaceagainst which a saw or other cutting device uses as a guide;

FIG. 2A is a drawing of a curved saw blade according to the invention;

FIG. 2B is a drawing of an alternative saw blade according to theinvention, preferably including a right-angle bend;

FIG. 3A is a drawing which depicts a trial/cutting guide having flatsurfaces as opposed to curved surfaces adapted for articulation within ajoint;

FIG. 3B is a drawing which depicts a trial/cutting guide havingtruncated surfaces corresponding to chamfer cuts;

FIG. 3C is a drawing which depicts a trial/cutting guide having arounded surface;

FIG. 4A is a drawing which illustrates a method of approaching box cutsfrom a distal perspective;

FIGS. 4B and 4C depict alternative ways in which distal and posterioraugment cuts may be made from the side, whether laterally or medially;

FIG. 5 shows a device for determining the joint line relative to a tibiausing the fibula as reference;

FIG. 6A is a drawing which shows a wedge-shaped defect often encounteredin distal femur bone loss; and

FIG. 6B is a drawing which shows a combination trial and cutting guidehaving “non-parallel” slots and wedges as part of a bone-loss conformingmethod of resection.

DETAILED DESCRIPTION OF THE INVENTION

The present invention extends and, in certain instances, improves uponapparatus and methods disclosed and claimed in U.S. Pat. No. 5,716,361,which issued Feb. 10, 1998, entitled BONE CUTTING GUIDES FOR USE IN THEIMPLANTATION OF PROSTHETIC JOINT COMPONENTS. Accordingly, the entirecontents of this patent are incorporated herein by reference. Broadly,the '361 patent relates to combination trial/cutting guides, and methodsof using the same, in various orthopedic joint situations such as theknee, hip, shoulder, and other areas of the body. The apparatus residesin a shaped body having an inner surface adapted for temporary placementagainst a bone surface and an outer surface configured to co-act in ajoint, for example, as part of a trial reduction. The present inventionis directed toward apparatus and surgical techniques which augment orsupplant certain teachings of the '361 patent with respect toalternative cutting fixtures and resection accuracy and stability. Thevarious aspects of the instant disclosure are broadly classifiedaccording to broad categories which follow.

Trial/Cutting Guide Stabilizers

In some instances, including those associated with femoral kneearthroplasty, the shaping of the cutting body to co-act in a joint mayresult in relatively thin thicknesses between the inner and outersurfaces of the body. As such, if surfaces or slots are provided for aparticular resection, the cutting tool may extend through the body ofthe device for only a short distance, resulting in a potentialinstability.

This aspect of the present invention is accordingly directed toward thelengthening of one or more of the cutting guides through the use ofremovable stabilizers which are temporarily attached to the body. Thisfeature builds upon concepts disclosed in reference to FIG. 6 of the'361 patent, in particular, which teaches the use of an extension blockto carry out box cuts. However, although the following discussion anddrawings reference a combination trial and cutting guide of the typedisclosed in this issued patent, it should be understood that theseremovable stabilizers are applicable to other bone-cutting situationsand, in fact, may be applied to cutting guides even if they are notshaped to function as a trial device.

As illustrated in FIG. 1, stabilizers 12 and 14 are temporarily andremovably attached to a cutting guide 10, thereby effectivelylengthening the surface against which a saw or other cutting device usesas a guide with respect to a resection procedure. The stabilizers mayinclude a single, extended flat surface such as that provided by block12, or may include slots, as shown with respect to block 14, or bothsurfaces and slots in combination with additional features.

The stabilizers may be temporarily affixed to the cutting guide in anumber of ways, including removable machine screws or Allen screws, ordetachable snaps which use pressure to apply and remove the members. Asa further alternative, a stabilizer such as 16 may include a featurewhich fits into an adjacent slot to provide temporary positioning. Theapplication of the stabilizers according to the invention is not limitedto the slots, openings or positions illustrated in the drawing, but maybe used in conjunction with any provided cutting surface. Procedurally,the method of use would follow that disclosed in the '361 patent, inthat a reduction would be performed and, upon a successful trial, theresections would be carried, as required, with the addition of theseslot extensions being used for further tool stabilization as disclosedherein.

Saw Blades for Effective Box-Cut Resections

In U.S. Pat. No. 5,716,361, slots and surfaces are provided to performbox cuts of the type associated with a cruciate-sacrificing procedure.Apparatus and methods are shown whereby even the bottom of the box couldbe at least partially formed by a slot or surface provided for suchpurpose. Although the end of the saw blade may eventually reach thesurface of an intramedullary stem, if so provided, upon removal ofinterfering portion later in the procedure, the beginning of the cutcould simply be extended, using the cut itself as a guide for theremaining portion of the resection.

As shown in FIG. 2A, a curved saw blade 22 may be provided such thatwhen the stem 24 is approached from above or below, additional materialon either side of the stem will be more effectively removed, therebyforming nearly the entire bottom of the box even with the stem in place.As an alternative to posterior-anterior slot orientation, a different orsupplemental set of slots may be provided to approach the bottom cutfrom the side of the trial-guide body. As shown in FIG. 2B, a saw 26having a right-angle blade may be provided, such that and with thetrial/cutting guide in place and with the knee flexed, any remainingportion(s) of the bottom of the box may be approached from the side.

Geometric Trial/Cutting Guides

A different aspect of this invention is directed toward trial/cuttingguides which do not necessarily include articulating outer surfaces toco-act in a joint. That is, in contrast to certain of the devices andtechniques disclosed in U.S. Pat. No. 5,716,361 wherein, for example,condylar surfaces are provided to co-act in a joint, so long as bothsides of the joint have surfaces which mate to properly determine gapsor distances, such surfaces which conform to human anatomy need not beprovided as a prelude to a trial joint reduction.

As shown in FIGS. 3A–3C, trial/cutting guides may be provided havingsurfaces geometrically indexed to a final implant, as opposed tocomplex, curved articulating surfaces, and still function to establish adesired orientation as part of a trial joint reduction. As long as theopposite side of the joint is configured to mate with these flatsurface, the surgeon may reduce this assembly into the joint to test forproper joint action, including extension/flexion gaps in the case ofknee-replacement surgery. With the trial/cutting guide is in position,it may be moved around so as to mate with the corresponding jointsurface and then pinned into place once a desired orientation has beenestablished. After flexing, the cuts associated with the joint may bemade with the cutting guide and, in the event that augments arerequired, these may be provided in conjunction with a trial or a final,as appropriate.

Although FIG. 3A shows a primary distal flat section which is connectedto a stem and an anterior section, the apparatus may include a posteriorsection as depicted with the arrow. In such a case, when the joint isflexed, this posterior piece may rest against the tibial portion tostabilize the entire assembly for resection as shown in the small insetdrawing. Nor do the test surfaces need to be flat or joined at rightangles. As shown in FIG. 3B, the outer surface 38 may be truncated in amanner corresponding to the “chamfer” cuts or, alternatively, as shownin FIG. 3C, the outer surface 39 may be rounded off without having toform complex condylar surfaces, for example, so long as a geometricindex is established with respect to the prosthesis ultimately installedin terms of joint line, flexion/extension gaps, degree of varus/vulgus,or some combination of these or other criteria. One advantage of thesealternative configurations is that joint geometry and movement may betested for accuracy, but the apparatus may be much more easy tomanufacture with the flat surfaces as opposed to highly complex surfacesused to provide natural joint features.

Alternative Cutting Approaches and Guide Marking

In performing cruciate sacrificing knee-replacement surgery, so-calledbox cuts are used to accommodate an intercondylar protrusion. To makethe sides of the box cuts, slots may be provided from anterior toposterior, as shown in U.S. Pat. No. 5,716,361. As an alternative,however, slots may be provided as shown in FIG. 4A to approach thesecuts distally. Although such a capability is disclosed in the form of anaperture in the '361 patent, slots may alternatively be provided, asshown.

FIGS. 4B and 4C depict alternative ways in which the distal andposterior augment cuts may be made from the side, whether laterally ormedially. FIG. 4B shows how a standard trial may be employed with orwithout other slots or cutting guides. In addition, a removableattachment guide may be temporarily attached to the side of the trial,as shown, to perform the distal cuts. The removable attachment guide maybe located at different positions, depending upon the augments that willbe used on the final.

As a further alternative, instead of a guide attachment, indicators maybe provided along various edges or other points of the cutting guidebody itself, enabling the surgeon to mark the bone, whether or not aspart of a trial reduction, remove the cutting guide body, and performthe cuts in a conventional manner (i.e., with standard cutting guides).The advantage here, however, is that with the trial in place thesemarkings would indicate precisely where the final implant will be fixedto the bone, whether augments are required or not. FIG. 4C illustrates asimilar concept, except for the posterior cuts, in the sense that astandard trial could be used but again facilities could be providedwhereby either a saw guide could be clipped on or the bone could bemarked for the posterior and anterior cuts in the manner just describedfor the distal cut.

Fibula Referencing

FIG. 5 depicts a different aspect of the invention, including a devicefor determining the joint line relative to the tibia, using the fibulaas reference. The device, labeled ‘A’, contacts the head or proximalportion of the fibula. The device preferably includes a transverseextending rod which is used to estimate where the joint line should berecreated relative to a deficient tibial surface. The vertical portionlabeled ‘X’ may be adjustable or fixed. Adjustability allows the jointline to be estimated and adjusted relative to a different sizedindividual. This could be estimated from an x-ray or other means.

In addition, an element may be provided on the transverse bar ‘Y’, toassure a transverse positioning, such as a bubble within a fluid ascommonly provided with a level, this of course would be more involvedthan just a simple transverse bar or any other such configuration wouldbe appropriate as well.

Bone-Loss Conforming Slots and Augments

Now making reference to FIG. 6A, it is often the case that bone lossoccurs primarily with respect to a central portion of the bone, leavingouter edges with a greater volume of bone stock remaining intact. Asshown in FIG. 6A, such is typically the case with the distal femur,resulting in a defect which is often wedge-shaped, as shown. Withtraditional cutting guides that produce transversely-aligned surfaces,it is often the case that this abundance of medial and lateral remainingbone is simply resected and lost for the sake of geometric simplicity.

As shown in FIG. 6B, a different aspect of this invention is theprovision of non-parallel slots and corresponding wedges, which may beused to retain at least some of this outer remaining bone material. Thatis, instead of making the traditional straight across distal cut 62, asshown in FIG. 6A, the cutting guide of FIG. 6B is instead used to makethe cuts along lines 64 and 66 thereby retaining the tips of the outerportions of the bone. In the event that wedges are required to fill thegaps between the prosthetic element and the surfaces created throughthese non-parallel slots, the wedges, too, are also wedge-shaped, asshown in FIG. 6B. Although the specific example depicted has to do withthe distal femur, it should be noted that the apparatus and methods areuseful in any situation which would benefit from an oblique cut and/orcorresponding wedges to conserve bone stock where, in the past,straight-across cuts have been used at the expense of such bonematerial.

1. A method of shaping a bone to receive a prosthesis having anarticulating surface with a medial condyle and a lateral condyle,comprising the steps of: providing a combination trial and cutting guidehaving an inner surface and an outer surface, the inner surface beingshaped for conformance with a bone to be modified, and the outer surfacelacking a medial condyle and a lateral condyle but being geometricallyindexed to the articulating surface of the prosthesis; performing atrial joint reduction including the bone having the combination trialand cutting guide temporarily installed thereon; shaping the bone withthe cutting guide so that the prosthesis will achieve a desiredorientation in accordance with the geometric indexing; removing thecombination trial and cutting guide; and affixing the prosthesis to thebone.
 2. The method of claim 1, wherein the bone is a distal femur. 3.The method of claim 1, wherein the outer surface is substantiallyplanar.
 4. The method of claim 1, wherein the prosthesis is associatedwith cruciate-sacrifice joint-replacement surgery, and wherein the stepof shaping the bone, includes the step of performing one or moreintercondylar box cuts.
 5. The method of claim 4, further including thestep of providing a bone-cutting saw having a concave curved distal endto perform at least one of the box cuts.
 6. The method of claim 4,further including the step of providing a bone-cutting saw having a bentblade to perform at least one of the box cuts.
 7. The method of claim 4,further including the step of referencing the fibula to determine thedesired orientation.